Polycyclic aromatics by two-stage hydrodealkylation



May 2, 1967 w, s. GREEN ETAL POLYCYCLIC AROMATICS BY TWO-STAGE HYDRODEALKYLATION Filed April 14, 1965 205400 10b@ 055200200 Y mzmmzmxa 0C0 zi.; 5191 m 0N, mmomaoma -m0 0m 00 .200 0 s 00. 200891 0m 4^ tz: W tz: 292.5.. z0F 5 u -moomn i -gomez mzmzwza v s @200mm vu mmm J. D i .l D l H. H om u vm m m 0m m o w v M 00 w 0050000 *il Il m a 0`. l. @G Ezoma 092205 a i; w mmsz. uw 5005 m0 AIMIV 0m mziz wwmmovm wzwznz m 0 S .E 05 z mmzJ 6050000 @05E m 0 200040291 02001542010 5005 zi.; 520.. 5059.@ zomooo nited States Patent O 3,317,623 v POLYCYCLIC AROMATICS BY TWO-STAG HYDRODEALKYLATION William Sidney Green, Huntington, W. Va., and Charles D. Hoertz, Jr., Ashland, Ky., assignors to Ashland Orl & Refining Company, Houston, Tex., a corporation of Kentucky Filed Apr. 14, 1965, Ser. No. 448,063 49 Claims. (Cl. 260-672) The present invention relates to the dealkylation of hydrocarbons and the product thereof. In a more specic aspect, the present invention relates to a method of pretreating a dealkylation feed stock and the product of such pretreatment. In a still more specific aspect, the present invention relates to a method for the dealkylation of hydrocarbons involving a preconditioning dealkylation step.

In the prior art it has been well known to obtain mononuclear and polynuclear aromatic hydrocarbons from various sources. One such source of aromatics is a coal tar fraction. The coal tar fraction contains some aromatics which are unsubstituted and, therefore, useful as such, if they can be adequately separated from irnpurities, such as, carbazole and sulfur containing compounds, and substituted aromatics having substituent groups, such as, methyl and ethyl groups. It is also known that the alkyl substituted aromatics may be dealkylated to improve the product yield. Other sources of aromatics, in addition to coal tar distillates, include tar sands, shale oil, bone oils, wood tar and other naturally occurring materials. Still another source of aromatics is the various products resulting from processes for refining liquid petroleum oils. Since liquid petroleum oils are basically made up of the same components as tar sands, shale oils and the like, except for quantities of components and the form of the crude product, large amounts of aromatics occur in petroleum oils, depending upon their origin, and, as a result, large amounts of impure aromatics and aromatic precursors are obtained as products of various processes for refining petroleum oil to produce the usual ultimate product-gasoline. As indicated, most refinery streams containing substantial amounts of aromatics are impure streams and the aromatics must be separated from parainic, naphthenic and other types of hydrocarbons. One method of making this separation involves the use of aromatic selective solvents, such as, furfural and the like. Such selective solvents, however, also separate alkylated aromatics, which were previously referred to as aromatic precursorsA As is the case with coal tar distillate fractions, the alkylated aromatics in petroleum oil streams include both mononuclear and polynuclear alkyl substituted materials. In addition, the substituent groups include one or more methyl groups, ethyl groups and the like. Accordingly, in order to produce aromatics in commercial yields, it is necessary to convert the alkylated aromatics to unsubstituted products. This conversion is generally carried out by dealkylating the substituted aromatics generally by what is known as a hydrodealkylation operation. In such hydrodealkylation methods, the feed stock is treated at high temperatures with hydrogen or hydrogen producing compounds in the presence of a catalyst in order to selectively split off the alkyl group or groups. This process is especially well suited for the dealkylation of mononuclear and polynuclear aromatics. Such hydrodelakylation operations may be carried out at temperatures between 800 and 1500 F. Higher yields can generally be obtained by operating at or near the upper temperature limits. These upper temperature limits are also advantageous when operating on comparatively high boil- 3,317,623 Patented May 2, i967 ing feed stock materials. The major difficulty, however, in all hydrodealkylation processes, even at low temperatures, is the formation of carbon and coke during the reaction. This carbon and coke formation is generally considered to be the result of scission or rupturing of aromatic rings at high temperatures or under severe conditions to form tar or coke precursors, as well as from the tar and coke precursors present in the feed stock itself. Again, higher boiling feed stocks will generally contain much higher quantities of coke and tar precursors. This formation of tar and coke in the hydrodealkylation process results in a rapid plugging and deactivation of the catalyst and the frequent necessity of shutting down the operation to clear the catalyst and regenerate it. This frequent and time-consuming shutdown, clean up and regeneration obviously results in an expensive and a highly inefficient overall operation.

Polynuclear aromatic materials higher than naphthalene, e.g. phenanthrene, have-been difficult to produce by prior art techniques in substantially pure form. Up to the present time the principal source of phenanthrene has been a coal tar distillate or anthracene oil (green oil) fraction, usually boiling between 300 and 360 C. Phenanthrene is used in making dyes, is a stabilizer for explosives and smokeless powder and has been used in the synthesis of pharmaceuticals, drugs and organic intermediates. As previously indicated, prior art techniques for recovery of phenanthrene have included selective solvent extraction with furfural, carbon disulfide and the like, as well as selective crystallization and selective absorption. However, the separated products have at best been in poor yields of marginally poor products.

It is therefore an object of the present invention to provide an improved technique for the preparation of a hydrodealkylation feed stock. A further object of the present invention is to provide Van improved technique for the removal of tar and coke precursors from hydrodealkylation feed stocks. Another and further object of the present invention is to provide an improved technique l,for the preparation lof a hydrodealkylation feed stock from high boiling catalytically cracked products. Yet another object of the present invention is to provide an improved technique for the preparation of a hydrodealkylation feed stock from a cracked slurry oil. A further object of the present invention is to provide an improved technique for the preparation of a hydrodealkylation feed stock from a catalytically cracked cycle oil. Yet another object of the present invention is to provide an improved technique for the preparation of a hydrodealkylation feed stock from a mixture of catalytically cracked cycle oil and slurry oil. Another and further object of the present invention is to provide an improved technique for the preparation of a hydrodealkylation feed stock which technique involves a preliminary hydrodealkylation of the feed stock under mild conditions. Still another object of the present invention is to provide an improved technique for the preparation of hydrodealkylation feed stock wherein a hydrocarbon fraction containing aromatic precursors is oxidized at an elevated temperature an'd the oxidized product is preliminarily hydrodealkylated at mild conditions. Still another object of the present invention is to provide an improved technique for the preparation of a hydrodealkylation feed stock -wherein a hydrocarbon fraction containing aromatic precursors is treated with an aromatic selective solvent and the extracted aromatics are thereafter oxidized at an elevated temperature and the oxidized aromatic material is finally hydrodealkylated under mild conditions. Another object of the present invention is to provide an improved hydrodealkylation process in which a selectively treated feed stock is employed. Yet another object of the present invention is to provide an improved hydrodealkylation process in which a high boiling catalytically cracked fraction is selectively treated prior to hydrodealkylation. A further object of the present invention is to provide an improved hydrodealkylation process in which a catalytically cracked slurry oil is pretreated prior to hydrodealkylation. Another object of the present invention is to provide an improved hydrodealkylation process in which catalytically cracked cycle oil is selectively pre-treated prior to hydrodealkylation. A still further object of the present invention is to provide an improved hydrodealkylation process in which a mixture of catalytically cracked cycle oil and slurry oil is selectively pretreated prior to hydrodealkylation. Another object of the present invention is to provide an improved hydro'dealkylation process in which a hydrodealkylation feed stock is preliminarily hydrodealkylated under mild conditions. Another and further object of the present invention is to provide an improved hydrodealkylation process in which a hydrocarbon fraction containing alkylated aromatics is oxidized at an elevated temperature and the oxidized aromatics are then preliminarily hydrodealkylated under mild conditions. A further object of the present invention is to provide an improved hydrodealkylation process in which a hydrocarbon fraction containing aromatic precursors is treated with an aromatic selective solvent, the extracted aromatics are oxidized at an elevated temperature and the oxidized aromatics are then preliminarily hydrodealkylated under mild conditions. Yet another object of the present invention is to provide an improved hydrodealkyltaion process in which the hydrodealkylation feed stock is hydrodealkylated under relatively mild conditions and a portion of the product of the first hydrodealkylation is thereafter hydrodealkylated under much more severe hydrodealkylation conditions. Another lobject of the present invention is to provide an improved hydrodealkylation feed stock. Another object of the present invention is to provide an improved unsubstituted aromatic composition. Another and further object of the present invention is to provide an improved aromatic product, including naphthalene and higher boiling aromatics. Still another object Iof the present invention is to provide a polynuclear aromatic product of improved purity. Yet another object of the present invention is to provide an improved aromatic product rich in phenanthrene and fluorene. Another object of the present invention is to provide a phenanthrene product of high purity. These and other objects and advantages of the present invention will Ibe apparent from the following detailed description when read in conjunction lwith the accompanying drawing. The drawing is a flow diagram of the preferred technique for preparation of a hydrodealkylation feed stock, hydrodealkylation of the feed stock and the production of a substantially pure unsubstituted aromatic product.

The present invention is applicable to any hydrocarbon product of petroleum or coal tar origin, containing signicant amounts of aromatics, specically, mononuclear and polynuclear compounds having substituent alkyl groups and, particularly the higher boiling mononuclear and polynuclear materials, such as, dimethylphenanthrenes, methylphenanthrenes, alkyl fluorenes and alkylnaphthalenes. While alkyl benzenes can be treated in accordance with the present invention, it has found its most effective use in the production of phenanthrene, uorene and naphthalene. Accordingly, the present invention is most useful in treating hydrocarbon materials boiling above about 550 F.

One source of mixtures of these materials has been product streams from petroleum refining operations, such as, catalytic reforming, hydroforming, cracking, etc. Such processes yield large amounts of alkylated aromatics. While such alkylated aromatics may be utilized in motor fuels and other products as such, greater demand for these products exists in the pure chemical field where a highly puried material is desired for -use as solvents and chemical intermediates. By way of specific example, product streams obtained by fractionating the liquid product of a uid catalytic cracking process produce feed stocks which benefit most significantly by the use of the present treatment.

Referring specifically to the drawings, a cracked product from a fluid catalytic cracking unit is fed to fractionator 10 through line 12. In fractionator 10 the uid catalytic cracking product is separated into a light gasoline fraction which is discharged through line 14, a gasoline product discharged through line 16 and a #2 fuel oil product discharged through line 18. These three materials, of course, have direct uses in industry and further reference thereto is unnecessary. In addition to the above, the remaining or bottoms of the fractionation operation is split into what is called a cycle oil, normally having a boiling point of about 600 to 700 F. and a higher boiling slurry oil, normally having a boiling range of about 650 to 850 F. The cycle oil is discharged from fractionator 10 through line 20 and the slurry oil through line 22. Both of these materials are rich in alkyl aromatics, such as alkyl phenanthrenes and, by the same token, because of their high boiling points, also contain substantial amounts of coke precursors of generally unknown composition. Speculatively, these coke precursors include indene and the like and, to a great extent, act like olefins and polymerize readily. Preferably, the slurry oil is clarified, as by settling, distillation or other means. However, this conventional operation is not shown so that the drawings will not be unduly complicated.

The slurry oil and/or the cycle oil are fed to furfural extraction unit 24 through the continuation of cycle oil line 20, or, if slurry oil alone is utilized through slurry oil branch line 26. Furfural is fed to extraction unit 24 through line 28. This extraction operation selectively removes aromatics from parainic, naphthenic and other non-aromatic components. The solvent-to-oil volume ratio utilized should be in the neighborhood of 0.2:1 to 2:1. This, of course, can be readily selected by one skilled in the art. While furfural has been given as a solvent, other suitable solvents include phenol, methanol, acetonirile, dimethylforamamide and others. From extraction unit 24, byproduct rafiinate is discharged through line 30. The mixture of aromatic extract, plus furfural, passes through line 32 to stripper 34. In stripper 34 the furfural is removed by distillation and discharged through line 36. A highly concentrated aromatic mixture is discharged through line 38. This mixture will normally have a boiling point of about 600 to 850 F., more or less, depending of course upon the nature of the starting material.

The concentrated aromatic mixture passing from stripper 34 through line 38 is fed to oxidizer unit 40. While the specific example pertains to the treatment of cycle oils and slurry oils, it should also be recognized that any aromatic concentrate of petroleum origin can be utilized. In some cases, as with highly aromatic petroleum mixtures, such as reformer bottoms, the previously described fractionation, extraction and stripping operations would be unnecessary and the aromatic mixture could be fed directly to oxidizer unit 40 through line 42. Oxidizer unit 40 is supplied with air, oxygen or oxygencontaining material through line 44. In oxidizer unit 40 the aromatic mixture is subjected to air-blowing or oxidizing conditions, such as those normally used for air-blowing or oxidizing asphalts and asphaltic fractions. Illustrative conditions for use in the Oxidation unit include a temperature of about 475 to 500 F., a pressure from atmospheric pressure to about p.s.i.g., and an air velocity of approximately 0.1 to 0.5 cubic feet per minute per gallon of aromatic mixture. The oxidation is carried out to a softening point of at least about 50 to about 300 F. and preferably to about 50 to about 150 F. Measurements of softening point, and its significance as a measurement of the degree of oxidation of asphalt,

are well-known to those skilled in the art. It should be recognized, however, that the higher the softening point above about 150 F., the more difficult it becomes to process the oxidized aromatic mixture. At present, it is thought most desirable to oxidize until the aromatic mixture has a softening point in the range of about 50 to about 100 F. in order that the coke precursors may be substantially removed while producing a useable tar pitch. During such oxidation the aromatics of the character of alkyland unsubstituted-phenanthrene remain relatively stable whereas the coke precursors tend to condense and polymerize to products of substantially higher boiling points.

Oxidized aromatic mixture from oxidizing unit 40 is discharged through line 46 to fractionator 48 where it is fractionated or stripped to remove the above-mentioned higher boiling coke precursors. Specifically, vacuum distillation is preferred. The oxidized aromatic mixture is fractionated or stripped, in fractionator 48 to produce a pretreated hydrodealkylation feed stock which is discharged through line 50. The hydrodealkylation feed stock is substantially free of materials boiling above about 740 F. and preferably the hydrodealkylation feed stock has an end boiling point falling in the range of about 690 to 740 F. The heavier fraction or higher boiling pitch fraction is discharged through line 52. This pitch fraction, as well as the hydrodealkylationI feed stock which is a primary stream, has been found to have highly desirable properties when derived from petroleum fractions, as indicated. The pitch fraction obtained from petroleum based aromatic mixtures has been found to have characteristics and properties very closely resembling or surpassing those of pitch fractions obtained from coal tar and, as such, has numerous industrial uses.

The pretreated hydrodealkylation feed stock passing through line 50 is fed to a first hydrodealkylation unit 54. As previously indicated, the feed stock to first hydrodealkylation unit 54 may be any hydrodealkylation feed stock rich in high boiling alkyl aromatic materials and particularly a material rich in phenanthrene precursors, such as, dimethylphenanthrene. Such hydrodealkylation feed stock from an external source may be fed to first unit 54 through line 56. Preferably, however, the feed stock to unit 54 is pretreated feed stock passing through line 50. Hydrogen is supplied to unit 54 through line 58. It is also desirable to inject water (stream) along with or separately from the hydrogen. The injected steam ap pears to reduce the temperature necessary for a given degree of conversion. Either the pretreated hydrodealkylation feed stock or a feed stock from an external source can, if desired, be desulfurized by known techniques prior to its introduction to unit 54. This desulfurization operation is conventional and well known to those skilled in the art and for this reason is not specifically illustrated in the drawings.

Hydrodealkylation unit 54 may be any conventional apparatus adapted for contacting gases and liquids with solids. For example, fixed, circulating and fiuid bed contactors having single or multiple beds may be employed. Such contactors may be operated according to various modes, such as batch, cyclical or continuous. In a continuous operation, a catalyst in granular, powdered or pelleted form is contacted countercurrently or concurrently while owing through the reactor, ordinarily by gravity flow, with restricted streams of reactant gases and liquids. Heat may be supplied by suitable preheating of the catalyst or by internal or external heating of the reactor itself and/ or by preheating the feed fluids. Contact time and heat supplied may be regulated by suitably adjusting the flow rate of catalyst and feed materials. In a cyclic operation a plurality of stationary beds of catalyst are ordinarily employed, whereby some of the units may be maintained on stream at all times, while others are undergoing regeneration or cleaning. Heat is ordinarily supplied externally or by internal heating elements, and

the operation may be conducted at atmospheric pressure or above. In accordance with the preferred embodiment of the invention, a fixed bed reactor unit is employed. Fresh or regenerated catalyst is held stationary in the reactor and the feed is passed downwardly through the bed under pressure on a continuous basis. If coke or carbon builds up in the bed, the pressure drop across the bed increases. When the pressure drop and carbon content of the bed reach levels which are either inconvenient or impossible to contend with, the bed is no longer usable and the reactor is shut down. Then, the catalyst is either regenerated in the reactor or is removed and replaced with fresh catalyst. Because the invention has the effect of minimizing the production of carbon in the catalyst bed, the above described mode of operation is quite simple and eminently practical because the reactor requires only infrequent shutdowns on account of carbon formation in the catalyst bed and such shutdowns do not constitute a serious interruption of production, considering their infrequency.

The hydrodealkylation carried out in unit 54 is carried out at relatively mild conditions with respect to the conditions practiced in the hereinafter-mentioned second hydrodealkylation unit. By mild conditions, it is meant that the temperature of reaction and/ or the residence time are controlled. These two conditions are most effective in controlling the severity of the hydrodealkylation reaction. However, it should be recognized that other conditions, as well as the type of catalyst, can be varied as between the first and second hydrodealkylation operations and some control over the severity of the reaction can be exercised in this way. In any event, it is believed that this mild treatment, under otherwise conventional hydrodealkylation conditions, in some way serves to convert coke and carbon precursors to materials which can be readily separated from the higher boiling alkyl aromatics which are to be subsequently converted to non-alkylated materials. By the same token, this first hydrodealkylation or stabilization does not, to any appreciable extent, affect or destroy the precursors of phenanthrene and higher boiling aromatic materials. However, it should be recognized that this analysis of what takes place in the first hydrodealkylation unit 54 is purely theoretical and it is not desired that the present invention should be limited by any particular theory.

In the operation of alkylation unit S4, a weight-hourly space velocity between 0.2 and 2.0 can be employed, although 0.5 to 1.0 is preferred. The pressure utilized may also vary over a wide range from O to 1000 p.s.i. However, the preferred operating pressure is between about 400 and 800 p.s.i. The hydrogen to feed stock mole ratio may range from 10:1 to 30:1, but is preferably from 10:1 to 20:1. By contrast with the conditions hereinafter discussed with regard to the second hydrodealkylation operation, the temperature employed in accordance with the present invention in unit 54 is between 1000 and 1200 F. and preferably between l075 and 1125 F. The residence time should be between about 0.05 and 0.5 minute and is preferably between 0.1 and 0.3 minute. As previously indicated, these conditions appear to have a stabilizing effect on the hydrodealkylation feed stock and produce preconditioned hydrodealkylation feed stock which can then be subjected to a hydrodealkylation operation under conditions which are much more severe than those previously employed. However, it should again be emphasized that such severe conditions do not result in the formation of large quantities of coke and carbon when operating on such a preconditioned feed stock.

As indicated previously, any good hydrodealkylation catalyst may be employed in unit S4. However, it has been found that a catalyst having chromic oxide as an active ingredient is best suited for use in unit 54. A -chromic oxide catalyst found to give excellent results is a catalyst trade designated G-41 and available commercially from The Girdler Construction Company. X-

ray diffraction analysis shows the chromic oxide to be present in the form of hexagonal crystals, as distinguished from chromia-aluminum co-gel catalysts. The total chromic oxide content of the commercial product is calculated at 11.8% Cr203 by weight, the remainder of the product being a high purity, low sodium content, gamma type alumina.

According, preconditioned hydrodealkylation feed stock from unit 54 is passed through line 60 to fractionator 62. Fractionator 62 serves to separate the high-boiling condensed and polymerized coke .precursors from the feed stock m-aterials. The lower boiling materials in the feed stock, e.g. those boiling below about 725 F., may be handled in a variety of ways. All of the lower boiling materials may Ibe passed to a second hydrodealkylation unit 66. Alternatively, separate fractions of said lower boiling materi-als may be obtained from the fractionator, such as a side cut fraction rich in phenanthrene and alkyl phenanthrenes and a fraction boiling lower than phenanthrene. Any one or more of such separate fractions are then separately hydrodealkylated to produce unsubstituted aromatics. In accordance with the preferred ernbodiment of the invention, the fractionator 62 is used to discharge through line 69 a side cut boiling in the range of about 575 to 725 F. and containing phenanthrene and alkylated polycyclics boiling higher than phen-anthrene. Tarry, polymerized coke and carbon precursors boiling above about 725 F. are taken from the fractionator as bottoms through line 68. Light ends boiling below about 575 F. are taken off through line 64. The side cut obtained through line 69 contains the bulk of the aromatics which are to be dealkylated in hydrodealkylation unit 66. It is considered advantageous to include the phenanthrene in the side cut, since, during the dealkylation which takes place in unit 66, other materials having boiling points close to that of phenanthrene are converted to materials with different boiling points, thus facilitating subsequent recovery of high purity phenanthrene.

Hydrodealkylation unit 66 is preferably of the same type as unit 54 and to a great extent is operated under substantially the same conditions. It is provided with a hydrogen line 70 and steam injection may be employed. Also, the weight-hourly space velocity, the pressure and the hydrogen to feed stock ratio may be substantially the same as those employed in unit 54. However, the ternperature and the residence time are substantially more severe in unit 66. A temperature difference of at least 75 F., are preferably between 75 and 350 F., should be employed. For example, unit 66 is oper-ated at a temperature between about 1275 to 1350 F., and preferably at 1300 to 1315 F. The residence time is between 0.2 and 0.8 minute and is preferably between 0.3 and 0,-4 minute.

Catalysts which have been found highly useful in accordance with the present invention have the following analyses and properties:

Chemical, wt. percent, dry basis:

This catalyst is called Nalcoden'by its manufacturer, Nalco Chemical Company.

The product from second hydrodealkylation unit 66 is passed through line 72 to stripper 74. It has been found that this product is an extremely clean product and that unit 66 is substantially free of coke and carbon in spite of the severe conditions utilized. The product from unit 66 is separated in stripper 74 to produce a gaseous component comprising principally hydrogen, and hydrocarbon gas, mostly methane, which is discharged through line 76.v The remaining aromatic concentrate is discharged from stripper 74 through line 78. This aromatic concentrate is a valuable product as such, but may be subjected to further fractionation in fractionating unit 80. Fractionating unit may separate the aromatic concentrate into individual components or groups of components, depending upon the use to which the product is to be put. Forexample, a cut boiling below naphthalene may be separated and discharged through line 82. Naphthalene maybe separated and discharged through line 84. The highest yboiling fraction or a fraction boiling -above phenanthrene may be separated and discharged through line 86. In addition, a highly valuable and concentrated phenanthrene product may also be separated and discharged through line for further treatment or use. The material boiling between naphthalene and 4phenanthrene may be separated as a single aromatic concentrate or split into a plurality of individual aromatic materials as illustrated by discharge line 92 of fractionator 80.

The following examples illustrate the outstanding results which have been obtained in accordance with the present invention.

Example I A slurry oil fraction from a fluid catalytic cracking unit is extracted with furfural and the separated aromatic material is oxidized to a softening point of about to F. A pitch fraction is removed by precipitation with a praffinic solvent and the remaining pretreated hydrodealkylation feed stock is fed to a first hydrodealkylation unit. This reactor comprises a 3A" diameter chamber made of Schedule 8O stainless steel. The reactor is filled to a bed depth of about 81/2" with Girdler G-41 catalyst `previously described. The following conditions are maintained during the hydrodealkylation reaction: temperature between 1090 and 1115 F., weight-hourly space velocity about 0.95, pressure about 400 p.s.i., hydrogen to liquid feed stock mole ratio about 13:1 and residence time about 0.2 minute. The product from this treatment is obtained in a yield of about 81% based on the weight of the feed stock, and of this product, about 11% is phenanthrene.

The preconditioned feed stock is then fed to a fractionator operating at a 10:1 reflux ratio. This fractionator is a Todd-column batch distillation unit. The phenanthrene and lower boiling materials are removed from the preconditioned feed stock leaving a material boiling in the range of about 640 F. to about 725 F. as a feed for the second hydrodealkylation operation.

In the second stage of hydrodealkylation the same reactor is utilized and this reactor is filled to a bed depth of about 81/2 with the previously described Nalcoden catalyst. The following conditions are maintained during the course of the second or more severe hydrodealkylation operation: temperature between 1300 and 13l5 F., weight-hourly space velocity 1.09, pressure 400 p.s.i., hydrogen to hydrocarbon mole ratio 20:1, and residence time about 0.35 minute. The product yield in this particular instance is found to be 74.6% based on the weight of the feed to the hydrodealkylation unit. Upon subsequent fractionation, this product is found to contain about 56% of phenanthrene. Most significantly, however, the final product is extremely clean and neither of the two reactors shows any signs of detrimental carbon or coke formation after extended periods of use.

9 Example Il The procedure of Example I is repeated, except that after the first hydrodealkylation step, the resultant preconditioned feedstock is fractionated to produce a heart cut boiling in the range of about 575 F. to about 725 F., light ends boiling below about 575 F. and bottoms boiling above about 725 F. The heart cut is then subjected to a second stage of hydrodealkylation as above described. The product yfrom the second hydrodealkylation step is readily fractionated to produce phenanthrene of high purity.

While specific examples have been given herein and specic illustrations set forth, it is to be recognized that these recitals are made only in an effort to teach those skilled in the art a preferred operation in accordance with the present invention. Accordingly, it is to be understood that the present invention is to be limited only by the appended claims.

We claim:

1. A method of preparing a hydrodealkylation feed stock, comprising: extracting aromatics from a liquid hydrocarbon fraction containing alkylated aromatics and boiling above about 600 F.; oxidizing said extracted aro matics at an elevated temperature and for a time Suthcient to produce a softening point between about 50 F. and 300 F.; separating a low boiling fraction boiling below about 740 F. from a higher boiling fraction containing coke precursors; subjecting said low boiling fraction to hydrodealkylation under relatively mild conditions including a temperature below about 1200 F. and in the presence of hydrogen and a hydrodealkylation catalyst; and separating from the product of said hydrodealkylation a hydrodealkylation feed stock boiling below about 725 F. and substantially free of coke precursors.

2. A method of preparing a hydrodealkylation feed stock, comprising: oxidizing a liquid hydrocarbon fraction containing alkylated aromatics and boiling above about 600 F. at an elevated temperature and for a time sufficient to produce a softening point between about 50 F. and 300 F.; separating a low boiling fraction boiling below about 740 F. from a higher boiling fraction containing coke precursors; subjecting said low boiling fraction to hydrodealkylation under relatively mild conditions including a temperature below about 1200 F. and in the presence of hydrogen and a hydrodealkylation catalyst; and separating from the product of said hydrodealkylation a hydrodealkylation feed stock boiling below about 725 F. and substantially free of coke precursors.

3. A method of preparing a hydrodealkylation feed stock, comprising: subjecting a liquid hydrocarbon fraction containing alkylated aromatics and boiling above about 600 F. to hydrodealkylation in the presence of hydrogen and a hydrodealkylation catalyst; maintaining the reaction conditions of said hydrodealkylation below the level at which any appreciable quantity of alkylated aromatics boiling above about the end point of phenanthrene and anthracene is dea-lkylated including a temperature below about l200 F; and separating from the product of said hydrodealkylation a hydrodealkylation feed stock boiling below about 725 F. and substantially free of coke precursors.

4. A method in accordance with claim 3 wherein the liquid hydrocarbon fraction is a fraction boiling between 600 and 850 F.

5. A method in accordance with claim 3 wherein the liquid hydrocarbon fraction is a slurry oil from a catalytic cracking operation.

6. A method in accordance with claim 3 lwherein the liquid hydrocarbon fraction is a heavy cycle oil from a catalytic cracking operation.

7. A method in accordance with claim 3 wherein the liquid hydrocarbon fraction is a mixture of slurry oil and heavy cycle oil from a catalytic cracking operation.

8. A method in accordance with claim 3 wherein the catalyst employed contains chromic oxide as an active ingredient.

9. A method in accordance with claim 3 wherein the catalyst employed is chromic oxide on an alumina carrier.

10. A method in accordance with claim 3 wherein the temperature of the reaction is between about 1000 and 1200 F.

11. A method in accordance with claim 3 wherein the temperature of the reaction is between 1075 and 1125 F.

12. A method in accordance with claim 3 wherein the residence time of the reaction is between 0.05 and 0.5 minute.

13. A method in accordance with claim 3 wherein the residence time of the reaction is between 0.1 and 0.3 minute.

14. A method in accordance with claim 3 wherein the weight-hourly space velocity of the reaction is between 0.2 and 2.

15. A method in accordance with claim 3 wherein the weight-hourly space velocity of the reaction is between 0.5 and 1.

16. A method in accordance with claim 3 wherein the pressure of the reaction is between 0 and 1000 p.s.i.

17. A method in accordance with claim 3 wherein the pressure of the reaction is between 400 and 800 p.s.i.

18. A method in accordance with claim 3 wherein the mole ratio of hydrogen to liquid hydrocarbon utilized in the reaction is between 10:1 and 30: 1.

19. A method in accordance with claim 3 wherein the mole ratio of hydrogen to liquid hydrocarbon utilized in the reaction is between 10:1 and 20: l.

20. A method in accordance with claim 3 wherein the hydrodealkylation feed stock ,is a material boiling above about 640 F.

21. A hydrodealkylation feed stock obtained by subjecting a liquid hydrocarbon fraction containing alkylated aromatics and boiling above about 600 F. to hydrodealkylation in the presence of hydrogen and a hydrodealkylation catalyst; maintaining the reaction conditions of said hydrodealkylation below the level at which any appreciable quantity of alkylated aromatics boiling above about the end point of phenanthrene and anthracene is dealkylated including a temperature below about l200 F; and separating polymeric material from the product of said hydrodealkylation to produce a hydrodealkylation feed stock boiling below about 725 F. and substantially free of coke precursors.

22. A hydrodealkylation feed stock in accordance with claim 21 wherein the liquid hydrocarbon fraction is a fraction boiling between 600 and 850 F.

23. A method for dealkylation of a liquid hydrocarbon fraction, comprising: subjecting a hydrocarbon fraction containing alkylated aromatics and boiling above about 600 F, to a iirst hydrodealkylation under relatively mild conditions and in the presence of hydrogen and a hydrodealkylation catalyst; separating from the product of said rst hydrodealkylation a lower boiling fraction boiling below about 725 F. and a higher boiling fraction containing coke precursors and subjecting the lower boiling fraction to a second hydrodealkylation under more severe conditions including a temperature lat least about 75 F. above that utilized in said first hydrodealkylation and in the presence of hydrogen and a hydrodealkylation catalyst.

24. A method in accordance with claim Z3 wherein the catalyst employed in the first hydrodealkylation contains chromic oxide as an active ingredient.

25. A method in accordance with claim 23 wherein the catalyst employed in the first hydrodealkylation is chromic oxide on an alumina carrier.

25. A method in accordance with cla-im 23 wherein the catalyst in the second hydrodealkylation contains molybdic trioxide and cobalt oxide as active ingredients.

27. A method in accordance with claim 23 wherein the catalyst in the second hydrodealkylation is molybdic trioxide and cobalt oxide on a carrier of silica-alumina.

28. A method in accordance with claim 23 wherein the temperature of the first hydrodealkylation is between 1000 and 1200 F.

29. A method in accordance with claim 23 wherein the temperature in the rst dealkylation is between 1075 and 1 125 F.

30. A method in accordance with claim 23 wherein the temperature in the second hydrodealkylation is between 1275 and 1350 F.

31. A method in accordance with claim 23 wherein the temperature in the second dealkylation is between 1300 and 1350 F.

32. A method in accordance with claim 23 wherein the temperature difference between the first and second hydrodealkylation is between 75 and 350 F.

33. A method in accordance with claim 23 wherein the residence time in the first hydrodealkylation is between 0.05 and 0.5 minute.

34. A method in accordance with claim 23 wherein the residence time in the first hydrodealkylation is between 0.1 and 0.3 minute.

35. A method in accordance with claim 23 wherein the residence time in the second hydrodealkylation is between 0.2 and 0.8 minute.

36. A method in accordance with claim 23 wherein the residence time in the second hydrodealkylation is between 0.3 and 0.4 minute.

37. A method in accordance with claim 23 wherein the weight-hourly space velocity in the first and second hydrodealkylation is between 0.2 and 2.

38. A method in accordance with claim 23 wherein the weight-hourly space velocity in the first and second hydro. dealkylation is between 0.5 and l.

39. A method in accordance with claim 23 wherein the pressure in the first and second hydrodealkylation is between and 1000 p.s.i.

40. A method in accordance with claim 23 wherein the pressure in the rst and second hydrodealkylations is between 400 and 800 p.s.i.

41. A method in accordance with claim 23 wherein the mole ratio of hydro-gen to aromatic hydrocarbon fin the first and second hydrodealkylations is between :1 and 30:1.

42. A method in accordance with claim 23 wherein the mole ratio of hydrogen to aromatic hydrocarbon in the first and second hydrodealkylations is between 10:1 and 1.

43. A method in accordance with claim 23 wherein the lower boiling fraction is a material boiling between about 625 F. to 725 F.

44. A method for dealkylation of a liquid hydrocarbon fraction comprising: oxidizingy a liquid hydrocarbon fraction containing alkylated aromatics and boiling above about 600 F. at an elevated temperature and for a time suicient to produce a softening point between about 50 F. and 300 F.; separating a low boiling fraction boiling below about 740 F. from a higher boiling fraction containing coke precursors; subjecting said low boiling fraction to a first hydrodealkylation under relatively mild conditions and in the presence of hydrogen and a hydrodealkylation catalyst; separating from the product of said first hydrodealkylation a hydrodealkylation feedstock boiling below about 725 F. and substantially free of coke precursors; and subjecting said hydrodealkylation feed- :stock to a second hydrodealkylation under more severe conditions including a temperature at least about 75 F. 4above that utilized in said first hydrodealkylation and in the presence of hydrogen and a hydrodealkylation catalyst.

45. A method for dealkylation of a liquid hydrocarbon fraction, comprising: extracting aromatics from a liquid hydrocarbon fraction containing alkylated aromatics and boiling above about 600 F.; oxidizing said extracted aromatics at an elevated temperature and for a time sufficient to produce a softening point between about 50 F. and 300 F.; separating a low boiling fraction boiling below about 740 F. from a higher boiling fraction containing coke precursors; subjecting said low boiling fraction to a first hydrodealkylation under relatively mild conditions and in the presence of hydrogen and a hydrodealkylation catalyst; separating from the product of said first hydrodealkylation a hydrodealkylation feedstock boiling below about 725 F. and substantially free of coke precursors and subjecting said low boiling fraction to a second hydrodealkylation under more severe conditions including a temperature at least about 75 above that utilized in said -rst hydrodealkylation and in the presence of hydrogen and a hydrodealkylation catalyst.

46. An aromatic product obtained by subjecting a hydrocarbon fraction containing alkylated aromatics and boiling above about 600 F. to a first hydrodealkylation under relatively mild conditions and in the presence of hydrogen and a hydrodealkylation catalyst; separating from the product of said rst hydrodealkylation a hydrodealkylation feedstock boiling below about 725 F. and substantially free of coke precursors; and subjecting said low boiling fraction to a second hydrodealkylation under more severe conditions including a temperature at least about 75 F. above that utilized in said first hydrodealkylation and in the presence of hydrogen and a hydrodealkylation catalyst.

47. An aromatic product in accordance with claim 46 wherein the liquid hydrocarbon fraction is a fraction boiling between 600 and 850 F.

48. An aromatic product obtained by oxidizing a liquid hydrocarbon fraction containing alkylated aromatics and boiling above about 600 F. at an elevated temperature and for a time sufficient to produce a softening point between about 50 F. and 300 F.; separating a low boiling fraction boiling below about 740 F. from a higher boiling fraction containing coke precursors; subjecting said low boiling fraction to a first hydrodealkylation under relatively mild conditions and in the presence of hydrogen and a hydrodealkylation catalyst; separating from the product of said first hydrodealkylation a hydrodealkylation feedstock boiling below about 725 F. substantially free of coke precursors; and subjecting said high boiling fraction to a second hydrodealkylation under more severe conditions than said first hydrodealkylation and in the presence of hydrogen and a hydrodealkylation catalyst.

49. An aromatic product obtained by extracting aromatics from a liquid hydrocarbon fraction containing alkylated aromatics and boiling above about 600 F.; oxidizing said extracted aromatics at an elevated temperature and for a time sufficient to produce a softening point between about 50 F. and 300 F.; separating a low boiling fraction boiling below about 740 F. from a higher boiling fraction containing coke precursors; subjecting said low boiling fraction to a rst hydrodealkylation under relatively mild lconditions and in the presence of hydrogen and. a hydrodealkylation catalyst; separating from the product of said rst hydrodealkylation a hydrodealkylation feedstock boiling below about 725 F. substantially free of coke precursors; and subjecting said high boiling fraction to a second hydrodealkylation under more severe conditions than said first hydrodealkylation and in the presence of hydrogen and a hydrodealkylation catalyst.

References Cited by the Examiner UNITED STATES PATENTS 2,778,780 1/1957 Romberg 208-4 3,075,022 1/1963 Gamrnon et al 260-672 3,108,063 10/1963 Chin et al 260-672 3,197,518 7/1965 Chapman et al 260-668 DELBERT E. GANTZ, Primary Examiner.

G. E. SCHMITKONS, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTEFICATE OF CORRECTION Patent No. 3 ,317 ,623 May 2 1967 William Sidney Green et al.

1t is hereby certified that error appears in the above numbered patent requiring correction and that the seid Letters Patent should reed es corrected below.

Column 4, line 40, after "given as a" insert specific example and is the preferred aromatic selective column 5, line 46, for "(stream)" read (Steam) column 7, line 8, for "According" read Accordingly line 49, for "are" read and column 8, line 39, for "praffinic" read paraffinc Signed and sealed this 5th day of November 1968.

(SEAL) Attest:

Edward M. Fletcher, Ir. EDWARD I. BRENNER Attesting Officer Commissioner of Patents 

3. A METHOD OF PREPARING A HYDRODEALKYLATION FEED STOCK, COMPRISING: SUBJECTING A LIQUID HYDROCARBON FRACTION CONTAINING ALKYLATED AROMATICS AND BOILING ABOVE ABOUT 600*F. TO HYDRODEALKYLATION IN THE PRESENCE OF HYDROGEN AND A HYDRODEALKYLATION CATALYST; MAINTAINING THE REACTION CONDITIONS OF SAID HYDRODEALKYLATION BELOW THE LEVAL AT WHICH ANY APPRECIABLE QUANTITY OF ALKYLATED AROMATICS BOILING ABOVE ABOUT THE END POINT OF PHENANTHRENE AND ANTHRACENE IS DEALKYLATED INCLUDING A TEMPERA-
 6. A METHOD IN ACCORDANCE WITH CLAIM 3 WHEREIN THE LIQUID HYDROCARBON FRACTION IS A HEAVY CYCLE OIL FROM A CATALYTIC CRACKING OPERATION. 